1. Field of the Invention
The present invention relates, in general, to a ceramic condenser composition and, more particularly, to a dielectric ceramic composition for boundary layer condensers, improved in both dielectric properties and insulation resistance properties. The present invention also relates to a method for preparing the same.
2. Description of the Prior Art
Generally, a boundary layer condenser is manufactured through very intricate procedures, including various formulations and processes. In particular, conventional manufacturing procedures and compositions for improving dielectric properties are very diverse.
A boundary layer condenser is required to exhibit a superior dielectric constant, low dielectric loss and superior insulation resistance. Research and development efforts have been directed to improve each of these properties without deleteriously affecting the others, as well as to improve two or three properties simultaneously. However, a dielectric ceramic composition satisfying these properties has not yet been reported.
In dielectric ceramic compositions comprising SrTiO.sub.3, generally WO.sub.3 and Bi.sub.2 O.sub.3 are used as dopants to make SrTiO.sub.3 semiconductive. If SrTiO.sub.3 is subjected to solid phase sintering, large stresses are induced. Accordingly, it is preferred to sinter such dielectric ceramic compositions in a liquid phase. However, since WO.sub.3 has a melting point greater or equal to 1,470.degree. C, it is not liquified when SrTiO.sub.3 is sintered, which deleteriously affects the resulting product. Bi.sub.2 O.sub.3 has a melting point of about 825.degree. C, so that it forms a liquid phase when SrTiO.sub.3 is sintered. However, Bi.sub.2 O.sub.3 does not sufficiently reduce SrTiO.sub.3. Kenton Derek Budd, "Processing and properties of tungsten-doped strontium titanate ceramics" Master Thesis, Univ. of Illinois at Urbana-Champaign, 1981; A.K. Mehrotra, "Microstructure and Dielectric Behavior for Pure and Bismuth-doped SrTiO.sub.3 Polycrystalline Ceramics" PH.D. Thesis, Univ. of Illinois at Urbana-Champaign, 1982.